Control of particle supply of blasting apparatus

ABSTRACT

The invention relates to a method for adjusting or operating a particle-metering system for a particle blasting installation, in particular a blasting installation for the working of surfaces, the abrasive throughput of which is preset by means of a passing-through opening that can be varied on the basis of time and/or variables and is determined by means of a downstream throughput sensor as a throughput sensor signal (DS), wherein the throughput sensor signal (DS) is used for controlling a manipulated variable (SG) for the degree of setting of the passing-through opening, wherein to adjust the metering system for at least one value of the manipulated variable (SG) the actual throughput (D) through the passing-through opening is determined by means of a measurement of the weight of abrasive material (M) allowed through within a defined time period (Dt), and the manipulated variable (SG), the actual throughput (D) and the corresponding throughput sensor signal (DS) are stored in an assignment table, wherein the relations between the actual throughput (D), the manipulated variable (SG) and the throughput sensor signal (DS) are used during subsequent operation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US-national stage of PCT applicationPCT/EP2016/000110 filed 21 Jan. 2016 and claiming the priority of Germanpatent application 102015000632.0 itself filed 22 Jan. 2015.

FIELD OF THE INVENTION

The invention relates to a method of adjusting or operating aparticle-metering system of a particle-blasting apparatus, particularlyof a blasting apparatus for treating a surface where the particlethroughput is preset by a feed orifice that can be varied with respectto time and/or variables and is determined by a downstream flow sensorgenerating a flow-sensor signal (DS), with the flow-sensor signal (DS)being used to control a manipulated variable (SG) for the output settingof the feed orifice.

In a particle-blasting apparatus used particularly for treating asurface, the particle throughput that is outputted to a workpiece forthe purpose of working it is controlled via a feed assembly. This feedassembly is generally between a supply vessel in which the blastingparticles is held and a system through which the blasting particles isaccelerated and guided toward a workpiece. A compressed-air system or animpeller wheel is usually used to accelerate the blasting particles. Dueto irregularities in the throughput of the blasting particles throughthe feed assembly, the particle throughput that is fed to the workpiecemay not be constant. Such fluctuations in the particle throughput can becaused by nonuniform flow characteristics or other changing physicalconditions during operation of the blasting apparatus.

To compensate for fluctuations in the throughput, a device is proposedin DE 102014201913 [US 2014/0220861] in which the particle throughput ismaintained constant by variably controlling the opening of a valve inorder to increase or reduce the throughput that is measured by adetection device. In this case, a baffle plate sensor is used as adetection device for determining the particle throughput from thedeflection of a deflectable member, and the electrical characteristicsof the particle material are unimportant in this measurement method. Thesignal of the baffle plate sensor is used to control how much the valveis opened, and the flow cross section is varied mechanically such that aconstant quantity of blasting particles per unit of time is supplied.This principle for controlling the particle throughput is also used in acomparable manner with other detection devices and variable feedorifices.

However, the drawback of this solution is that, when the composition ofthe blasting particles changes and the physical characteristics changeas a result, the detection device measures a throughput value that doesnot match the actual throughput. As a result, the right quantity ofblasting particles for the blasting process is not fed to the workpiece.A change in the composition of the blasting particles can be broughtabout deliberately by changing the type of blasting particles, or it canchange inadvertently as a result of contaminants or modification of theblasting particles as a result of repeated use.

Particularly in a particle-blasting apparatus used in a production lineand in which a precise quantity of blasting particles is needed for theprocess, this constitutes a problem, since a change in the particlethroughput has an impact on the processing quality.

OBJECT OF THE INVENTION

It is the object of the invention to overcome this drawback and toprovide a method of adjusting or operating a feed assembly of a blastingapparatus whereby the feed assembly can be adjusted with minimalpersonnel and time and the particle throughput that is in fact requiredduring operation is directly ensured.

SUMMARY OF THE INVENTION

This object is achieved by a method in which, in order to adjust thefeed assembly for at least one manipulated variable (SG), the actualthroughput (D) through the variable feed orifice is determined bymeasuring the weight of the outputted blasting particles (M) within adefined time period (Dt), and the manipulated variable (SG), the actualthroughput (D), and the corresponding flow-sensor signal (DS) are storedin an allocation table, with the relationships between the actualthroughput (D), the manipulated variable (SG), and the flow-sensorsignal (DS) being used during subsequent operation.

The generation of the allocation table offers the advantage that amanipulated variable (SG) can be preset during the operation of the feedassembly following adjustment that corresponds to the actual requiredthroughput (D). As a result, the particle throughput through the feedassembly takes on the required value, thus ensuring the desiredprocessing quality during the blasting process.

In an advantageous embodiment of the invention, a functional correlationis calculated between the manipulated variable (SG) and the actualthroughput (D) from the allocation table generated during theadjustment, in which, for a discrete number of values for themanipulated variable (SG), the corresponding actual throughput (D) andthe corresponding flow-sensor signal (DS) are stored. As a result, amanipulated variable (SG) is extrapolated that corresponds or comesclosest to the respective actual required throughput (D) even if a valueis required for the actual throughput that is not stored as a discretevalue in the allocation table. Consequently, an appropriate manipulatedvariable (SG) is available for controlling the feed orifice for everyrequired throughput (D) that can be outputted by the feed assembly.

Likewise, in another advantageous embodiment of the invention, theactual throughput (D) is calculated from the allocation table as afunction of the flow-sensor signal (DS). This makes it possible todetermine the actual throughput (D) at least approximately for ameasured flow-sensor signal (DS) that is not stored in the allocationtable. The actual throughput (D) can thus be determined directly duringoperation from the flow-sensor signal (DS) and used to control orindicate and/or record the actual throughput (D).

In an advantageous embodiment of the invention, in order to calculatethe manipulated variable (SG) as a function of the actual throughput (D)and to calculate the actual throughput (D) as a function of theflow-sensor signal (DS), a linear extrapolation is performed between thediscrete values of the allocation table. This is a simple mathematicaloperation that can be performed with little computing power and cantherefore be carried out relatively quickly during control with orwithout feedback.

In another advantageous embodiment of the invention, the manipulatedvariable (SG) as a function of the actual throughput (D) and the actualthroughput (D) as a function of the flow-sensor signal (DS) isapproximated by a polynomial. In order to at least roughly approximatethe polynomial to the discrete values of the allocation table, it isnecessary to use at least a second-order polynomial. It was found thatapproximation by a fourth-order polynomial usually ensures an adequateapproximation to the discrete values of the allocation table withrelatively little computing power. In another advantageous embodiment ofthe invention, besides approximation using a polynomial, the discretevalues of the allocation table are correlated using a polynomialcalculation. This is also an arithmetic operation that is associatedwith reasonable computational complexity and enables an adequateapproximation to the discrete measured values of the allocation table.

In an advantageous embodiment of the invention, in order to adjust thefeed assembly, the manipulated variable (SG) is altered by a program indiscrete steps, and the actual throughput (D), the flow-sensor signal(DS), and the respective manipulated variable (SG) are stored in theallocation table for each discrete step.

Preferably, the adjustment range of the manipulated variable (SG) isdivided into a defined number of equidistant steps, and the respectivevalues of the manipulated variable (SG) are triggered successively intime. The number of steps depends on the available adjusting time andthe required accuracy of the allocation, with a subdivision into ten ortwenty steps being preferred. In a preferred embodiment of theinvention, several measured values, each with a measuring time period(Dt), are recorded for each discrete step of the manipulated variable(SG), and the average of the measured values is stored in the allocationtable. This procedure enables the allocation table to be generatedautomatically, thus minimizing the personnel and time required for theadjustment.

When using blasting abrasives having different compositions and/orphysical characteristics, a corresponding allocation table is preparedfor each of the blasting abrasives used. During operation of theblasting apparatus, the corresponding allocation table is then used tocontrol the feed assembly with or without feedback. This ensures duringoperation, when there is a change to a blasting abrasive that is alreadyknown, no adjustment of the feed assembly need be carried out but therequired abrasive throughput will reach the workpiece to be processednonetheless.

To operate the blasting apparatus, the feed assembly is controlled atthe start of the blasting process such that the correspondingmanipulated variable (SG) is calculated for the actual requiredthroughput (D) from the allocation table that was defined during theadjustment and applied to the feed orifice. The manipulated variable(SG) of the feed orifice is then regulated with respect to the measuredflow-sensor signal (DS) such that the throughput remains constant. Thus,at the start of the blasting process, the desired quantity of blastingparticles is supplied during the operation of the feed assembly, so thatthe desired processing quality is achieved on the workpiece.Particularly when the workpiece is blasted for only very short periodsof time, this has the advantage that the required abrasive throughput issupplied almost instantaneously and then maintained at the requiredlevel.

In addition, the actual throughput (D) is determined during operation ofthe feed assembly based on the throughput signal (DS) from theallocation table. During operation, the actual throughput (D) is thuseither indicated via a display and/or recorded, and regulation isperformed to a required throughput level.

In another advantageous embodiment of the invention, environmentalconditions such as ambient temperature, air pressure, and air humidityare measured during operation and a correction value is determined fromthis measurement with which the flow-sensor signal (DS) and/or themanipulated variable (SG) from the allocation table are multiplied. Thealtered environmental conditions and their influence on the feedassembly are thus taken into account. Determination of the correctionfactor is based on a correlation between flow-sensor signal (DS) andmanipulated variable (SG) and the environmental conditions that isdetermined by measurement or calculated mathematically. This offers theadvantage of enabling behavior of the feed assembly that is dependent onenvironmental conditions to be compensated for.

In an advantageous embodiment of the invention, in a blasting apparatusthat is particularly integrated into a production line, a switch isperformed automatically between adjustment and operation by eitherfeeding the blasting particles onto a workpiece or into a collectingvessel. This makes it possible to still feed the desired quantity ofblasting particles to the workpiece during operation even when theblasting particles are changed or in the case of wear-related changes inthe blasting particles and the associated physical characteristics. Thisis advantageous particularly in production lines, since a quickeradjustment can be made, thus resulting in shorter down time.

During measurement of the actual throughput (D), the weight of theblasting particles (M) is measured in the present invention in anadvantageous manner by measuring the increase in the weight of acollecting vessel into which the blasting particles are fed or thedecrease in the weight of a supply vessel from which the blastingparticles are drawn. The measurement of the decrease in weight offersthe advantage that the weight of the blasting particles leaving thesupply vessel through the feed orifice is measured directly without atime delay until it reaches a collecting vessel. However, due to theimmense weight involved, the measurement of the decrease in the weightof the supply vessel has the disadvantage in the case of large and/orheavy supply vessels that the accuracy of the measurement is limited asa result. In this case, it is advantageous if any delays before thecollecting vessel is reached are conceded and the weight increase of thecollecting vessel is measured, since that is substantially smaller incorresponding measurement time periods (Dt) and can be measured moreeasily and with greater precision.

Advantageously, a certain throughput level is required in order to checkthe adjustment of the blasting apparatus, and the actual throughputthrough the feed assembly is determined by measuring the weight of theoutputted blasting particles (M) within a defined time period (Dt).During the check, an appropriate manipulated variable (SG) is calculatedfor the required throughput from the allocation table that was generatedduring the adjustment and applied to the feed orifice.

A direct check of the adjustment is performed immediately after theadjustment. If the throughput required in this case does not match withthe throughput that is actually measured, then it is necessary toregenerate the allocation table with a greater number of discrete stepsof the manipulated variable (SG) or to perform a more precisecalculation of the functional correlation between the values from theallocation table. A more exact calculation of the functional correlationis preferably performed through approximation with a higher-orderpolynomial. The direct check ensures that a precise adjustment has beencarried out before the operation of the blasting apparatus thatsatisfies the requirements.

A check of the adjustment is also advantageously performed after acertain period of operation during stoppages. In this case, if therequired throughput does not match with the actual throughput, thenanother adjustment with generation of the allocation table is necessary.Regular checking of the adjustment enables operation-related influenceson the feed assembly and changes in the blasting particles to be takeninto account and compensated for by readjustment. Performing a check hasthe advantage that the generation of a complete allocation table is onlydone as needed, which saves time and other resources.

The method described is preferably used in n particles-blastingapparatus having a supply vessel that is connected via a feed assemblyto an outlet. The feed assembly consists of a feed orifice that can bevaried with respect to time and/or variables and a flow sensor arrangeddownstream. In addition, the blasting apparatus has a collecting vesselwith a weight detector that receives the blasting particles from thefeed assembly. The feed assembly is connected to a processor thatregulates the feed orifice that can be varied based on time and/orvariables and reads out the flow sensor. In order to evaluate the weightdetector and control the processor, the latter is connected to acomputer. Through the use of a collecting vessel with a weight detector,the weight of the blasting particles is measured within a defined timeperiod, and the actual throughput is determined using the methoddescribed above. The corresponding regulation and control of the feedassembly is carried out by a computer in conjunction with the processor.

A mechanically adjustable flow section or a solenoid valve can be usedas the feed orifice that can be varied with respect to time and/orvariables. In the case of a ferromagnetic blasting abrasive, a solenoidvalve is preferably used in which the blasting particles are hindered byan applied magnetic field while flowing through the feed orifice andopened through the application of an additional compensating magneticfield. In the solenoid valve, the throughput is especially preferablyperformed by a pulse duration modification, with the on/off ratio beingproportional to the actuating variable.

To measure the throughput during operation, the flow sensor is amicrowave sensor, an ultrasonic sensor, a baffle plate sensor, aninduction sensor, or a capacitance sensor. Due to the simple and robustdesign, induction sensors or capacitance sensors are preferably used asflow sensors in the present invention.

In the case of blasting abrasive that has already been accelerated, itwas found that it is advantageous if, in addition to the collectingvessel, an upstream separator is used in which the blasting particlesare separated from other process materials and fed in its entirety intothe collecting vessel. A cyclone can be especially preferably used as aseparator in order to separate the blasting particles from the air. Inthis, the air is separated from the blasting particles and fed through afunnel into the collecting vessel. This is advantageous particularly ifthe blasting particles are already traveling at a high speed and simplyguiding it into the collecting vessel would distort the measuringresult. Using a separator, it is possible to switch between adjustmentand normal operation by inserting a deflector between the outlet and thefeed assembly that guides the blasting particles either into theseparator or onto the workpiece to be blasted. The deflector can beembodied as a robot that guides the outlet for the blasting particleseither into the separator or onto the workpiece. Such an arrangement canbe preferably converted into a production facility in which switching isperformed automatically between adjustment and operation. As a result,automated adjustment can be performed, which reduces the down times ofthe production facility.

The processor is connected to a computer, regulates the variable feedorifice, and reads out the flow sensor. Preferably, the processor has aneither digital or analog manipulated variable interface and a flowsensor interface in order to connect to the feed orifice and the flowsensor. In the analog design, the interfaces are additionally connectedby an analog-to-digital converter to a microcontroller that takes overcontrol of the feed assembly. The microcontroller stores the allocationtable in a memory and is connected to a digital computer interfaceand/or an interface to a machine control by means of which the processoris controlled. Such a processor makes it possible to integrate themethod of adjusting and operating a feed assembly of a blastingapparatus into a production line or to design it as a standalonesolution.

BRIEF DESCRIPTION OF THE DRAWING

Embodiments of the invention are illustrated in the drawing anddescribed in further detail below.

FIG. 1 shows a particle-blasting apparatus as it is used to adjust thefeed assembly, with the weight detector being connected to a collectingvessel;

FIG. 2 shows a particle-blasting apparatus as used to adjust the feedassembly, with the weight detector being connected to a supply vessel;

FIG. 3 shows the entries of the allocation table;

FIG. 4a shows a linear interpolation of the actual throughput (D) as afunction of the manipulated variable (SG);

FIG. 4b shows a flow-sensor signal (DS) as a function of the actualthroughput (D), which is approximated by a polynomial;

FIG. 5 shows a particle-blasting apparatus with integrated conversionbetween adjustment and operation; and

FIG. 6 shows an overview of a processor.

SPECIFIC DESCRIPTION OF THE INVENTION

FIG. 1 shows a particle-blasting apparatus 1 in which the blastingparticles 2 are held in a supply vessel and is delivered from same viaan outlet 4. The feed assembly 5, which consists of a feed orifice 6that can be varied with respect to time and/or variables, as well as adownstream flow sensor 7, is between the supply vessel 3 and the outlet4. The quantity of blasting particles 2 that leaves the supply vessel 3is predefined by the output setting of the feed orifice 6 and measuredby the flow sensor 7. For calibration, the blasting particles are fedinto a collecting vessel 8 and its weight (M) is measured by a weightdetector 9. An output of the weight detector 9 is evaluated by acomputer 10, and the throughput (D) through the outlet 4 is determinedas the weight of the blasting particles allowed to pass through within adefined time period (Dt). The output setting of the variable feedorifice 6 is predefined by the processor 11 as a manipulated variable(SG), with the processor 11 simultaneously also reading out theflow-sensor signal (DS) of the flow sensor 7. The feed assembly isadjusted by simultaneous measurement of the actual throughput (D) viathe weight detector 9 and measurement of the flow-sensor signal (DS) bythe flow sensor 7 with values for the manipulated variable (SG) of thefeed orifice 6 predefined by a program.

FIG. 2 shows another embodiment of the invention where, unlike theparticle-blasting apparatus 1 of FIG. 1, a weight detector 9 isconnected to the supply vessel 3. In this embodiment, the weight of theblasting particles that flows through the feed orifice 6 is determinedby having the weight detector 9 measure the decrease in the weight ofthe supply vessel 3. In contrast to the measurement of the increase inthe weight of the collecting vessel 8, this has the advantage that theweight is measured directly as the blasting abrasive flows out of theoutlet 4, and a time delay pending the arrival of the blasting particlesin the collecting vessel 8 is avoided. This arrangement is advantageousparticularly if the supply vessel and its contents have has a weightthat can be determined with sufficient accuracy without great effort andis therefore used in a particle-blasting apparatus in which a smallquantity of readied blasting particles suffices.

In an advantageous embodiment of the invention, the arrangement of aparticle-blasting apparatus 1 as in FIG. 2 is used exclusively foradjusting or checking a feed assembly 5. A feed assembly that is to beused in the future during operation is first inserted into aparticle-blasting apparatus 1 according to FIG. 2 between the supplyvessel 3 and the outlet 4, and an allocation table between themanipulated variable (SG), the actual throughput (D), and theflow-sensor signal (DS) is then generated and stored according to theabove-described method. The allocation table is then used during theoperation of the current feed assembly 5, which is for example installedin a production unit in order to control same with or without feedback.Due to the relatively small quantity of blasting particles required foradjustment, the decrease in the weight of the supply vessel 3 can beeasily measured during the adjustment, and a time-delay pending thearrival of the blasting particles in the collecting vessel 8 isirrelevant.

The recorded values of the actual throughput (D), the flow-sensor signal(DS), and the manipulated variable (SG) are stored in the allocationtable whose entries are shown in FIG. 3. The number of preset values ofthe manipulated variable (SG) is arbitrary and can be selected as afunction of the composition of the blasting particles, the required oravailable adjustment time, and the required precision. The allocationtable is stored in the processor 11 and/or in the computer 10. Duringoperation of the feed assembly 5 with a required actual throughput (D),the corresponding manipulated variable (SG) is read out from theallocation table, so that the actual required throughput is transmittedto the working process at the outlet 4 during operation. In addition,the allocation table is used during operation of the particle-blastingapparatus 1 to determine the actual throughput (D) from the measuredflow-sensor signal (DS) of the flow sensor 7.

FIG. 4a shows how a correlation between the manipulated variable (SG)and the actual throughput (D) is calculated from the discrete measuredvalues of the allocation table by linear interpolation. With the aid ofthis method, the manipulated variable (SG) is determined as a functionof the throughput (D), so that a value for the manipulated variable (SG)at an actual required throughput (D) is also available between thediscrete measured values.

FIG. 4b shows how a functional correlation between the throughput (D)and the flow-sensor signal (DS) is calculated from the discrete valuesof the allocation table through approximation via a polynomial. Theactual throughput (D) through the outlet 4 is determined from thisfunctional correlation from the measured flow-sensor signal (DS).

FIG. 5 shows a particle-blasting apparatus as used during operation. Theblasting particles 2 are located in the supply vessel 3 and passesthrough the feed assembly 5 toward an outlet 4, with a deflector 12between the outlet 4 and the feed assembly 5 that deflects the blastingparticles either into a separator 13 or onto a workpiece 14. In theseparator 13, the blasting particles are separated from other processmaterials and recovered completely by the collecting vessel 8. Theweight of the blasting particles (M) is measured by a weight detector 9.The throughput (D) through the feed orifice 6 is determined by thecomputer 10 by determining the weight of the blasting particles (M)emitted within a defined time period (Dt). In an advantageous embodimentof the invention, the blasting particles 2 are accelerated by an aircompressor 15, thereby achieving the desired process result during theblasting of the workpiece 14. The blasting apparatus 1 is integratedinto a production line by connecting the processor 11 to a higher-levelmachine control 16.

In an advantageous embodiment of the invention, the ambient conditionssuch as temperature, air pressure, and air humidity are measured by thesensor unit 17. The ambient conditions are compensated for duringoperation by multiplying the manipulated variable and/or the flow-sensorsignal from the allocation table by a correction function that isdependent on the ambient conditions.

In another advantageous embodiment of the invention, the collectingvessel 8 from FIG. 5 is embodied as a funnel-shaped collecting vessel onwhose funnel neck a check valve is mounted. At the end of the adjustmentprocedure, the check valve is opened and the blasting particles locatedin the funnel-shaped collecting vessel is guided into the collectingvessel 3 and supplied for further processing.

FIG. 6 illustrates an advantageous embodiment of the processor 11 thatcontrols the variable feed orifice 6 and reads out the flow sensor 7.For this purpose, the processor 11 has a manipulated variable interface18 for the manipulated variable and a flow sensor interface 19 for theflow-sensor signal (DS). These interfaces are either analog or digital.In an analogous embodiment, additional analog-to-digital converters 20are used in order to connect to a microcontroller 21. Themicrocontroller 21 has a memory 22 and/or is connected thereto; it ishere that the specific allocation table is stored and called up duringadjustment. The connection of the processor 11 to the computer 10 isachieved via a computer interface 23. In the case of integration into ahigher-level machine unit, a connection to the controller 16 is achievedvia a machine interface 24. In addition, the sensor unit 17 is read outvia an ambient sensor interface 27, and the ambient conditions oftemperature, air pressure, and air humidity are taken into account bythe processor 11 when controlling and/or regulating the feed assembly 5.

In an advantageous embodiment, the machine interface 24 has a digitalsignal for calling up the table, a digital enable signal for the feedorifice, an analog control signal, and an analog throughput signal.Using these signals, it is easy to integrate the processor into ahigher-level memory-programmable or computer-based controller.

In another embodiment, the manipulated variable interface 18 has anadditional digital enable signal that enables the opening of the feedorifice 6 as needed. An additional safety function is thus ensured andinadvertent releasing of the blasting particles prevented duringoperation.

In an advantageous embodiment, the processor 11 further comprises anoperator control module 25, which is provided to set operating modes ofthe processor, as well as a display unit 26 that displays the status ofthe processor 11 and outputs operating parameters. In this case, theweight detector is read out directly via the processor. This embodimentof the invention enables the processor to be operated without aconnection to a computer interface or to a higher-level controller.

In another advantageous embodiment, the processor 11 is advantageouslyintegrated physically into the feed assembly 5. This embodiment of theinvention offers the advantage that a connection between processor 11and feed assembly 5 via the manipulated variable interface 18 and theflow sensor interface 19 is not needed. A physically more compactconstruction is thus achieved.

In another advantageous embodiment of the invention, the controlfunction of the processor and the computer is taken over directly by amemory-programmable or computer-based higher-level controller. In thisembodiment of the invention, the corresponding interfaces to the feedassembly and to the weight detector as well as the memory for theallocation table are supplied by the higher-level controller. Such anembodiment of the invention enables simple integration of theabove-described method of operating or adjusting a feed assembly of aparticle-blasting apparatus, particularly in production lines, with theadjustment of the feed assembly being accomplished with minimum effortand with the actually required abrasive throughput being ensured duringoperation.

The invention claimed is:
 1. A method of adjusting or operating aparticle-metering system for a particle-blasting apparatus having a feedorifice of variable flow cross section through which abrasive particlespass via a feed assembly from a supply of the particles to an outlet,the method comprising the steps of: measuring particle throughputthrough the feed orifice by a downstream flow sensor generating aflow-sensor signal; using the flow-sensor signal to control amanipulated variable for an output setting of the feed orifice; in orderto adjust the feed assembly for a manipulated variable, determiningactual throughput through the feed orifice by measuring a weight ofoutputted particles within a defined time period; storing themanipulated variable, the actual throughput, and the correspondingflow-sensor signal as measured values in an allocation table; and usingrelationships between the actual throughput, the manipulated variable,and the flow-sensor signal during subsequent operation.
 2. The methoddefined in claim 1, further comprising the step, in order to adjust thefeed assembly, of: calculating the manipulated variable from themeasured values of stored in the allocation table as a function of theactual throughput.
 3. The method defined in claim 2, further comprisingthe step, in order to adjust the feed assembly, of: calculating theactual throughput from the measured values of the allocation table as aflow-sensor signal.
 4. The method defined in claim 2, further comprisingthe step of: calculating a functional correlation between themanipulated variable and the actual throughput as well as between theactual throughput and the flow-sensor signal by a linear interpolationbetween the values of the allocation table.
 5. The method defined inclaim 3, further comprising the step of: calculating a functionalcorrelation between the manipulated variable and the actual throughputas well as between the actual throughput and the flow-sensor signal asan at least second-order polynomial from the values from the allocationtable.
 6. The method defined in claim 1, further comprising the steps,in order to adjust the feed assembly, of: altering the manipulatedvariable by a program in discrete steps; and storing the actualthroughput, the flow-sensor signal, and the manipulated variable in theallocation table as the measured values for each step.
 7. The methoddefined in claim 1, further comprising the steps, in order to check theadjustment for a required throughput from the allocation table, of:determining the manipulated variable; applying the determinedmanipulated variable to the feed orifice; and comparing the actuallymeasured throughput to the required throughput.
 8. The method defined inclaim 1, further comprising the steps of: generating allocation tablesfor different particles that are used during the operation of theblasting apparatus to control the feed assembly.
 9. The method definedin claim 1, further comprising the step, during operation of the feedassembly with a required actual throughput, of: adjusting the feedorifice according to the corresponding manipulated variable from theallocation table.
 10. The method defined in claim 9, further comprisingthe step, during operation of the feed assembly, of: determining theactual throughput with respect to the flow-sensor signal from theallocation table prepared during the adjustment.
 11. The method definedin claim 1, further comprising the steps, during operation of the feedassembly, of: measuring ambient conditions including ambienttemperature, air pressure, and air humidity; and multiplying themanipulated variable or the flow-sensor signal from the allocation tableby a correction function dependent on the measured ambient conditions.12. The method defined in claim 1, further comprising the step of:switching automatically in a blasting apparatus between adjustment andoperation by feeding the particles either onto a workpiece or into acollecting vessel.
 13. The method defined in claim 1, further comprisingthe step, in order to determine the weight of the particles, of:measuring an increase in a weight of a collecting vessel into which theparticles are fed or a decrease in a weight of a supply vessel fromwhich the particles are fed.
 14. A particle-blasting apparatus fortreating a surface, the apparatus comprising: a supply vessel filledwith blasting particles; an outlet directable at the surface; a feedassembly between the vessel and the outlet and having a feed orifice ofvariable flow cross section; a downstream flow sensor generating anoutput corresponding to flow through the orifice; a weight detector thatdetermines the weight of the blasting particles passing through the feedassembly into a collecting vessel and generates an output correspondingthereto; and a processor that regulates the adjustable feed orifice inaccordance with the outputs of the flow sensor and of the weightdetector.
 15. The particle-blasting apparatus defined in claim 14,wherein the weight detector determining the weight of the blastingparticles passing through the feed assembly is connected to thecollecting vessel and measures any increase in weight thereof.
 16. Theparticle-blasting apparatus defined in claim 14, wherein the variablefeed orifice is a mechanically adjustable flow section or solenoidvalve.
 17. The particle-blasting apparatus defined in claim 14, whereinthe flow sensor is a microwave sensor, an ultrasonic sensor, a baffleplate sensor, or an induction sensor.
 18. The particle-blastingapparatus defined in claim 14, wherein the processor has amanipulated-variable interface and a flow-sensor interface forconnecting to the feed orifice, a microcontroller with memorycontrolling the processor and connected via a digital computer interfaceand/or a machine interface to a computer and/or a controller.
 19. Aparticle-blasting apparatus for treating a surface, the apparatuscomprising: a supply vessel filled with blasting particles; an outletdirectable at the surface; a feed assembly between the vessel and theoutlet and having a feed orifice of variable flow cross section; adownstream flow sensor generating an output corresponding to flowthrough the orifice; a weight detector that determines the weight of theblasting particles passing through the feed assembly into a collectingvessel, that is connected to the supply vessel to measure a decrease inweight thereof, and that generates outputs corresponding thereto; and aprocessor that regulates the adjustable feed orifice in accordance withthe outputs of the flow sensor and of the weight detector.
 20. Aparticle-blasting apparatus for treating a surface, the apparatuscomprising: a supply vessel filled with blasting particles; an outletdirectable at the surface; a feed assembly between the vessel and theoutlet and having a feed orifice of variable flow cross section; adownstream flow sensor generating an output corresponding to flowthrough the orifice; a weight detector that determines the weight of theblasting particles passing through the feed assembly into a collectingvessel and generates an output corresponding thereto; a processor thatregulates the adjustable feed orifice in accordance with the outputs ofthe flow sensor and of the weight detector; and an additional separatorbetween the feed assembly and the collecting vessel that separates theblasting particles from other process materials so that the blastingparticles reach the collecting vessel in its entirety.
 21. Theparticle-blasting apparatus defined in claim 20, further comprising: adeflector between the feed assembly and the outlet and guiding theblasting particles either into the separator or onto the workpiece to beblasted.